The present invention relates to a method of adjusting the axis of a car on-board radar, for example, used in a collision alarming system which measures a relative speed and a headway between a car of interest and an obstacle such as a preceding car by transmitting/receiving, for example, a radio wave, light or ultrasonic waves so as to inform a driver of approach to the obstacle and more particularly, to a car on-board radar axis adjusting method which, in a radar having an antenna mounted at a position offset from the longitudinal axis of a car (hereinafter simply referred to as a car axis), can perform the offset mount of the antenna with high precision and can perform the adjustment of mount angle of the antenna with ease.
In recent years, a millimeter wave radar serving as a headway measuring means of a headway alarming system has been studied and developed with the aim of preventing vehicle accidents. Generally, the directivity of transmitting axis of the antenna serving as a transmitting/receiving unit of the headway alarming system is considered as the fundamental condition for accuracy of radar measurement and stringent directivity is required. Accordingly, in a conventional antenna mounting method, when an electric field strength measuring unit of millimeter wave radar is mounted to the front of a car, the mount angle of an antenna is adjusted such that the measured strength of an electromagnetic wave radiated from the antenna is maximized for the purpose of correctly directing a beam radiated from the antenna along the car axis of the car.
JP-A-7-81490 proposes, as the aforementioned adjusting method, a technique for setting a mode in which the strength of a reflection wave electric field of an electromagnetic wave transmitted from a transmitter circuit of a radar is indicated in a receiver circuit of the radar and the mount angle of an antenna of the radar is adjusted such that the electric field strength is maximized.
The above prior art has, however, drawbacks as below. More particularly, in the first place, when the antenna mount angle is adjusted, the electric field strength of the reflection wave of the electromagnetic wave transmitted from the transmitter circuit of the radar must be indicated but generally, an indicator of the radar is not so constructed as to indicate the receiving electric field intensity, so that the aforementioned prior art cannot be used for the adjustment of the axis of general radars.
In the second place, the beam radiated from the antenna must be set so as to be correctly directed toward the running direction of a car of interest, that is, toward the car axis. When the antenna is mounted at an offset position apart from the car axis, the detected value must be adjusted by taking an offset amount into account. Especially, when a mono-pulse radar capable of detecting the azimuth angle in addition to the headway and relative speed between the car of interest and a leading car is concerned, the adjustment of the offset amount of antenna and antenna mount angle is a factor which has an important influence upon the accuracy of correct measurement of the azimuth angle. The conventional method is unsuited for the antenna mount angle adjustment in the mono-pulse radar.